Electric capacitor



March 28, 1967 M. H. PINTELL y 3,311,801;

ELECTRIC CAPACITOR Original Filed July 7, 1965 2 Sheets-Sheet l Mardi28, 1967 M. H. PINTELI. 3,311,801

ELECTRIC CAPACITOR original Filed July 7. 1965 2 shegts-sheet z f- H6.4g

United States Patent O 3,311,801 ELECTRIC CAPACITOR i Milton H. Pintell,Bronx, NX., assigner to Intron International, Inc., Congers, N.Y., acorporation of New York Continuation of application Ser. No. 470,059,July 7, 1965. This application June 23, 1966, Ser. No. 561,315 2 Claims.(Cl. 317-258) thermoplastic iilrns, have a dielectric constant whichappreciably vaiies with Itemperature so that, theoretic-ally, it ispossible to design capacitive circuit elements as temperature-responsivedevices adapted to perform a switching operation under predeterminedthermal conditions. An advantage `of such thermosensitive capacitorsover conventional thermistors is that, whereas Ythe latter dis-,

sipate electric energy which not only is lost to its intended vpurposebut-also is converted into heat liable to aifect the response of theelement, the condenser-type temperature detector is substantiallynondissipative. This advantage, however, is oifset in the case of knowndielectrics by the lack of even approximative linearity ot their thermalco- Veliicients, at least in those temperature ranges above and below C.which are of particular interest in practice. Moreover, thermistors haveapproximately semil-ogarithmic characteristics overV the most desirableranges and are, therefore, unsatisfactory for many applications asidefrom the self-heating effect.

It is, therefore, the general object of my present invention to providea thermosensitive capacitor Volf the character set forth which hasainearly linear characteristic of dielectric constant versustemperature, with a distinct positive slope, in a range from Well abovero-om temperature to substantially below freezing. l

A more particular object lof this invention is to provide a capacitorsatisfying lthe aforestated desiderata throughout a temperature rangeof, say, 54 C. to +125 C., this being an important performance range inmilitary specications. p

` A further object of this invention is to provide a highly flexibledielectric material endowed with the above-mentioned characteristics sothat condensers lniade with 'such material can' readilybe wound into`rolls or otherwise deformed to suit particular physical or electricalrequirements. v

Still another object of the instant invention is to provide an improvedelectrical capacitor and to exten-d the principles originally advancedin the above-mentioned oopending application.

As disclosed in my aforementioned application Ser, No. 98,357, a soli-ddielectric material of substantially linear characteristic Within arange of 0 C. to -l-100 C. and beyond, ire., with a substantially xedthermal coefcient of its dielectric constant (this coeiiicient being theslope of the characteristic), comprises a film of partially substitutedpolyvinyluoride, ie., a polymer in which only some of the hydrogen atomsof a vinyl chain are replaced by iluorine atoms. The present inventiondeals more particularly with the production of compounds according tothis formula and with specific compounds.

In my concurrently iiled copending application Ser. No. 470,058 Idisclose a dielectric material in film form which can be considered forpractical purposes to be a partially substituted polyvinyl fluoride inthe sense that 3 ,3 l 1,801 Patented Mar. 28, 1967 the material is acopolymer of vinyl -u-oride and an allylvinyl etherY so that the vinyluoride chain is interrupted by polymer segments which contain nohalogen. The allylvinyl ether can be methylvinyl, isobutylvinyl orVcetylvinyl ether and the proportion of uorine in the lm can rangebetween substantially 30 and 40% by Weight. Since commercially availablepolyvinyl uoride generally has a iluorine content of slightly above 41%by Weight, the copolymer includes between substantially 5 and 25 partsby weight of the allylvinyl ether together with to 75 parts by Weight ofvinyl fluoride.

It has been found that it is also possible to provide a iilm ofpartially substituted polyvinyl fluoride ultlling the physical andelectrical requirements of a dielectric material used fortemperature-sensitive electrical capacitors when the commerciallyavailable polyvinyl fluoride having a pure characteristic of variationof dielectric constant with temperature, is partially dehalogenated tohave a uorine content ranging between substantially 26% and 38% byweight, the starting material preferably being polyvinyl fluoride with ailuorine content of substantially 41.3% by weight. The dehalogenationprocess can be any of those suitable for dechl-orinating polyvinylchloride although care must be taken to terminate the dehalogenationstep prior to complete removal of uorine. The product of the uorinationstep can be dissolved in a solvent, preferably hot dimethylfformarnide,and cast into a lm with evaporation of the solvent.

The film has excellent physical properties from the point of view offlexibility and elongability, has a substantially linear temperaturecharacteristic olf dielectric constant and a relatively high breakdownvol-tage. The defluorina-tion process appears to create halogen-freeportions along the polymer chain which func-tion similarly to thenonhalogenate'd copolymer chain portions described in theabove-mentioned concurrently filed copending applic-ation.

Reference will now be made to the following specific examples andtheacompanying drawing wherein FIGS. 1-4 are a set of graphs representingthe dielectric constants o-f a variety of polyvinyl fluoride films,plotted as a function of temperature; and

F-I'G. 5 is a cross-sectional View through a capacitor according to thepresent invention. Y

The characteristic curves of FIGS. 1 4 wer-e all established with aconstant test frequency of 1000 cycles per second, in ranges from to+220 VC. as indicated along the abscissa. The ordinate 'represents thedielectric constant e of the materials involved. l f

FIG. l relates .to va standard polyvinyliiuoride l-m (commerciallyavailable under the name Teslar) With a uorine proportion of 4l.265% byWeight. Thisnoncopolymer tlm can be prepared as described by Kalb et al.in Journal of Applied Polymer Science, IV, 10, pp. 55 6i1 (1960). Thecharacteristic A1 of this ilm is of distinctly nonlinear shapeapproximating an S-curve, with a steeply sloping portion in the regionof 20 to +100 C. and lesser slopes on both sides of that region. Astraight line B1 intersects the curve A1 at points C1, D1 correspondingt-o 54 and +1125 C., curve A1 deviating appreci- 4ably from line B1 inthe range Cl-Dl by passing first below and then above that line.

In FIG. 2 Ik have shown a similar characteristic A2 intersected atpoints C2 and D2 by a straight line B2 from Vwhich it deviates only inone sense throughout the temportion being 37.08% 'by Weight. The film isproduced as described below.

In FIG. 3 I have shown the characteristic A3 of a partially deuorioatedpolyvinylfiuoride with the fluorine proportion reduced to'3`2.80% byweight. There is only a minor deviation of curve A3 from straight lineB3 between points C3 and D3.

I have shown in FIG. 4 a curve A4 which closely approaches a straightline B4, intersecting it at points C4, and D4, throughout thetemperature range of 54 to -l-l25 C.; curve A4 is the characteristic ofa partially defiuorinated polyvinyliiuoride, with the fluorineproportion amounting to 26.81% by weight.

FIG. 5 shows a capacitor 10 comprising a film 11 of partiallydefiuorinated polyvinylliuoride sandwiched between vapor-depositedelectrodes 12 and 13 to which terminals.14 and 15 are afiixed.

It will be apparentfrom the graphs of FIGS. l-4 that the partiallydeiiuorinated polyvinylfiuorides as a class, are superior asthermosensitive dielectric materials to ordinary polyvinylfiuoride film.

The films advantageously have a thickness between substantially 2.5M and0.08 mm., with a breakdown voltage ranging approximately from 12,000 to116,000 volts per millimeter of thickness.

EXAMPLE I Preparation partially substituted polyvinyl fluoride 3,00 g.of polyvinylfluoride polymer containing 41.265% Y iiuorine, weredissolved in 3000 g. of hot (120 C.) purified dimethylformamide, in a4,000 ml. reaction kettle. 715 g. of lithium aluminum hydride wereslowly added with mild agitation, and the mixture was then refluxed atthe lboiling point (153 C.) of dimethylforrnamide. The reactionproceeded smoothly. After 5 hours retiuxing, a sample of the partiallydehalogeriated polymer w-as re- Imoved and a fluorine determination onthe sample was made. The sample contained 37.08% uorine, indicating aloss of 4.18% fiuorine. Under comparable conditions refluxing for 11hours produced a polymer containing 32.80% fluorine or a loss of 8.46%fiuorine. Reiiuxing tor 23 hours produce-d a polymer containing 26.81%fluorine, or a loss of 14.45% iiuorine.

After reaching the desired fluorine content, the partially substituted,dehal-ogen'ated polymer solution was slowly poured, with vigorousagitation into 20 liters of hot (95 C.) water. A finely divided,slightly fibrous suspension of polymer formed. The polymer was recoveredby filtration an-d thoroughly washed with high-purity deionized water,until a sample of the wash water gave no indication of a risein'conductivity of the wash water. The washed partially substituteddehalogenated polymer was then dried at 80"V C. A white, finely-dividedpartially fibrous polymer was obtained.

' I EXAMPLE II lPreparation partially substtued polyvinyl fluoride 300g. of polyvinyliiuoride polymer, containing 41.2'65% (by weight)fiuorine, were dissolved in 3000 g. yof hot (120 C.) dimethylformamidein a 4-liter reaction kettle. 300 g. zinc clust, previously purified bytreating the dust in dilute hydrochloric acid, washed and dried,

was added to the polyvinyliiuoride solution. IThe mixture was slowlystirred and reliuxed at the boiling point (153 C.) of thedimethylformamide. After 3 hours and 45 minutes of refluxing, a sampleof the dehalogenated polymer was removed and a ffuorine determinationmade. Y

The sample contained 37.08% liuorine, indicating a loss :of 4.18%fluorine. Under comparable conditions, refluxing for 6 hours produced apolymer containing 32.64% fluorine, .or a loss of 8.622% fiuorine.Refluxing for a total of l5 hours produced a polymer containing 26.72%fiuorine or a loss of 14.54% fluorine.

rPhe hot solution was filtered to remove the unreacted zinc dust and thepartially substituted polymer solution was slowly poured with vigorousagitation into 20 liters offk Preparation of lms of partiallysubstituted polyvinyl fluoride 500 g. of partially substituted polyvinylfluoride, proyduced in accordance with Examples I and II, weredissolved, with stirring into 5000 g. of hot (120 C.) di;

methylforma-mide. The solution was fil-tered through a fibrous glassmat, and continuously cast onto a highly polished chromium-plated steeldrum 42 inches in diameter. The dimethylformalmide was evaporated fromthe p wet cast film, and the cast dry film was continuously strippedfrom the drum surface, and rewofund. Films ranging from 2.5;1. through12.5,a thickness were produced.

These films were slit to the desired widths, and employed to produce thethermally sensitive capacitor described.'

I claim: Y

1. A thermally sensitive electrical capacitor comprising la pair ofelectrodes separated by a film of partially defluorinated polyvinylfluoride with a liuorine content of 26 to 38% by weight of the polymer,said polymer being' composed exclusively of carbon, hydrogen andfluorine atoms.

2. An electrical component with a progressively varying impedance in atemperature range of a substantially --54 C. to |125 C. comprising acapacitor with `a substantially linear capacitance/temperaturecharacteristic throughout said range, said capacitor including a pair ofelectrodes separated by a film of partiallydefluorinated polyvinylfluoridewith a fluorine con-tent of 26 to 38%- by weight of the polymer,said polymer being composed Y.

exclusively of carbon, hydrogen and liuorine atoms.

References Cited by the Examiner UNITED STATES PATENTS 2,419,010 4/'1947Coffman. LEWIS H. MYERVS, Primary Examiner. E. GOLDBERG, AssistantExaminer,

1. A ATHERMALLY SENSITIVE ELECTRICAL CAPACITOR COMPRISING A PAIR OFELECTRODES SEPARATED BY A FILM OF PARTIALLY DEFLUORINATED POLYVINYLFLUORIDE WITH A FLUORINE CONTENT OF 26 TO 38% BY WEIGHT OF THE POLYMER,SAID POLMER BEING COMPOSED EXCLUSIVELY OF CARBON, HYDROGEN AND FLUORINEATOMS.